到目前为止我学到了什么
> Basics of point sprite drawing
> How to deal with point sprites rendering as solid squares
> How to alter orientation of a point sprite
> How to use multiple textures with a point sprite,越来越近了..
>这个sprite sprite sheet之前已经完成了,但只能在OpenGL ES 2.0(不是1.0)
这是我想要实现的图表
我在哪里
>我有一组工作点精灵都使用相同的单个方形图像.例如：一个16×16的圆形图像很棒.
>我有一个Objective-C方法,它生成一个含有多个图像的精灵图的600×600图像.我已经验证这是通过将整个sprite sheet图像应用于使用GL_TRIANGLES绘制的四元组.
>我已经使用上述方法成功地将精灵图的部分绘制到四边形.我只是不能让它与点精灵一起工作.
>目前,我正在生成纹理坐标,指向我所针对的精灵图片上精灵的中心.例如：使用底部的图像;星：0.166,0.5;云：0.5,0.5;心脏：0.833,0.5.
码：
顶点着色器
uniform mat4 Projection;
uniform mat4 Modelview;
uniform float PointSize;
attribute vec4 Position;
attribute vec2 TextureCoordIn;
varying vec2 TextureCoord;
void main(void)
{
gl_Position = Projection * Modelview * Position;
TextureCoord = TextureCoordIn;
gl_PointSize = PointSize;
}
片段着色器
varying mediump vec2 TextureCoord;
uniform sampler2D Sampler;
void main(void)
{
// Using my TextureCoord just draws a grey square,so
// I'm likely generating texture coords that texture2D doesn't like.
gl_FragColor = texture2D(Sampler,TextureCoord);
// Using gl_PointCoord just draws my whole sprite map
// gl_FragColor = texture2D(Sampler,gl_PointCoord);
}
我坚持的是什么
>我不明白如何在片段着色器中使用gl_PointCoord变量. gl_PointCoord最初包含什么？为什么？它在哪里获取其数据？
>我不明白要传递什么纹理坐标.例如,点精灵如何根据纹理坐标选择我的sprite sheet的哪一部分？我习惯于绘制有效的4组纹理坐标(每个顶点一个)的四边形,这有什么不同(显然是)？
解决方法
顶点着色器
uniform mat4 Projection;
uniform mat4 Modelview;
// The radius of the point in OpenGL units,eg: "20.0"
uniform float PointSize;
// The size of the sprite being rendered. My sprites are square
// so I'm just passing in a float. For non-square sprites pass in
// the width and height as a vec2.
uniform float TextureCoordPointSize;
attribute vec4 Position;
attribute vec4 ObjectCenter;
// The top left corner of a given sprite in the sprite-sheet
attribute vec2 TextureCoordIn;
varying vec2 TextureCoord;
varying vec2 TextureSize;
void main(void)
{
gl_Position = Projection * Modelview * Position;
TextureCoord = TextureCoordIn;
TextureSize = vec2(TextureCoordPointSize,TextureCoordPointSize);
// This is optional,it is a quick and dirty way to make the points stay the same
// size on the screen regardless of distance.
gl_PointSize = PointSize / Position.w;
}
片段着色器
varying mediump vec2 TextureCoord;
varying mediump vec2 TextureSize;
uniform sampler2D Sampler;
void main(void)
{
// This is where the magic happens. Combine all three factors to render
// just a portion of the sprite-sheet for this point
mediump vec2 realTexCoord = TextureCoord + (gl_PointCoord * TextureSize);
mediump vec4 fragColor = texture2D(Sampler,realTexCoord);
// Optional,emulate GL_ALPHA_TEST to use transparent images with
// point sprites without worrying about z-order.
// see: https://stackoverflow.com/a/5985195/806988
if(fragColor.a == 0.0){
discard;
}
gl_FragColor = fragColor;
}